1. Field of the Invention
The present invention generally relates to an apparatus and method for completing a wellbore. More particularly, the invention relates to an apparatus and method for expanding a tubular body in a wellbore. More particularly still, the invention relates to an apparatus and method for carrying a longer string of expandable tubular body in a wellbore.
2. Description of the Related Art
In well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill support member, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annular area is thus formed between the string of casing and the formation. The casing string is temporarily hung from the surface of the well. A cementing operation is then conducted in order to fill the annular area with cement. Using an apparatus known in the art, the casing string is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, the well is drilled to a first designated depth with a drill bit on a drill string. The drill string is removed. A first string of casing or conductor pipe is then run into the wellbore and set in the drilled out portion of the wellbore, and cement is circulated into the annulus behind the casing string. Next, the well is drilled to a second designated depth, and a second string of casing, or liner, is run into the drilled out portion of the wellbore. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then fixed, or “hung” off of the existing casing by the use of slips which utilize slip members and cones to wedgingly fix the new string of liner in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. As more casing strings are set in the wellbore, the casing strings become progressively smaller in diameter in order to fit within the previous casing string. In this manner, wells are typically formed with two or more strings of casing of an ever-decreasing diameter.
Decreasing the diameter of the wellbore produces undesirable consequences. Progressively decreasing the diameter of the casing strings with increasing depth within the wellbore limits the size of wellbore tools which are capable of being run into the wellbore. Furthermore, restricting the inner diameter of the casing strings limits the volume of hydrocarbon production fluids which may flow to the surface from the formation.
In the last several years, methods and apparatus for expanding the diameter of casing strings within a wellbore have become more common. For example, a string of liner can be hung in a well by placing the upper portion of a second string of casing in an overlapping arrangement with the lower portion of a first string of casing. The second string of casing is then expanded into contact with the existing first string of casing with an expander tool. The second string of casing is then cemented.
An exemplary expander tool utilized to expand the second casing string into the first casing string is fluid powered and run into the wellbore on a working string. The hydraulic expander tool includes radially expandable members which, through fluid pressure, are urged outward radially from the body of the expander tool and into contact with the second casing string therearound. As sufficient pressure is generated on a piston surface behind these expansion members, the second casing string being acted upon by the expansion tool is expanded past its point of elastic deformation. In this manner, the inner and outer diameter of the expandable tubular is increased in the wellbore. By rotating the expander tool in the wellbore and/or moving the expander tool axially in the wellbore with the expansion member actuated, a tubular can be expanded into plastic deformation along a predetermined length in a wellbore.
In one application, running tools used to expand the liner downhole typically support the liner weight on the face of the expander cone while running in the hole. This limits the maximum length of liner that can be run because the expansion cone shape is not designed to carry the liner. Rather, the expansion cone has a weight distribution and strength profile that enables the expansion cone to slide through the liner easily without being deformed. In addition to the risks involving the expansion cone, the running tool may prematurely shift and expand the liner. These design and operation problems lead to running shorter than desired lengths of liner.
This problem has been addressed by increasing the effective wall thickness of the liner at the support point against the expansion cone face to prevent yielding. However, the expansion cone has to apply more expansion force to expand a thicker liner wall. The increased tubular pressure may cause damage to other portions of the liner. As a result, this method is limited by the internal pressure rating of the expandable liner or its connections, and therefore, is still inadequate to provide the desired length of liner.
There is a need, therefore, for a reliable running and release mechanism to carry longer and heavier liners while running in the hole.